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Power Over Ethernet Interoperability Guide by Sanjaya Maniktala

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Practical Thermal Resistances
As an experiment, the standard 2s2p board was modified to test the impact of the two key additional PCB recommendations above—no grid under exposed pad, and generous copper filling, particularly on bottom layer for maximizing conduction and convection aided heat loss. However, other things were unchanged. The same-sized board was used in the same recommended JEDEC box, with the same position of thermocouple, and so on. A chip with a published 2s2p thermal resistance (junction to air) of 24°C/W, when placed on this 2s2p “look-alike board” showed a much improved thermal resistance of only 10.5°C/W.
The JEDEC board and the “look-alike board” created above were both large. What happens on a typical compact daughtercard, ...

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